At audio frequencies (i.e. between roughly 20 Hz to 20 kHz), passive transmission lines, such as speaker cables, may be considered equivalent to a simple circuit, as shown in FIG. 1A, with a cable 102 between an amplifier 100 or other signal source, and a speaker 104 or other signal destination. Such cables may be considered a multi-polarity cable, carrying two polarities of a signal, or a signal and reference ground, via two separate legs or conductors (which may comprise one or more individual conductors), as opposed to a single-polarity wire or cable comprising a single leg or conductor. The cable 102 has an internal and inherent resistance R, sometimes referred to as insertion loss; inductance L as combination of self-inductance of an individual conductor or leg and mutual inductance between two conductors; and capacitance C between conductors or separate legs.
High values for resistance, inductance, or capacitance can adversely affect transmission of the signal, in particular affecting high frequency response of the cable 102. However, these values are inter-related: in particular, mutual inductance between two conductors (such as two conductors in a parallel configuration, commonly referred to as zip cord) may be decreased by bringing the conductors closer together, but this increases capacitance between the conductors. Accordingly, typical cables 102 are designed to minimize one of these values, frequently inductance, at the expense of higher capacitance, which is considered to be relatively inaudible at low decibel losses (e.g. less than 3 dB within the audio range).
Unfortunately, beyond adverse effects on frequency response, high capacitance in a cable 102 may cause an amplifier 100 to oscillate at high frequencies, resulting in audible clipping or amplitude limiting of the output audio waveform, non-linear distortion, and potential damage to the amplifier 100. One work around, shown in FIG. 1B, is to include a Zobel network 106a-106b (sometimes referred to as a constant resistance network), which may be used to damp potentially harmful oscillations. However, the addition of such components add expense and potential for failure.